Since September 2017, all new passenger car models in the European Union (EU) are required to be type-approved following the Worldwide Harmonized Light Vehicles Test Procedure (WLTP), although existing models type-approved under the New European Driving Cycle (NEDC) procedure could still be registered until August 31, 2018. As a result, new vehicles coming to the market in 2018 were a mix of vehicles type-approved according to the NEDC or the WLTP. Based on preliminary 2018 CO2 monitoring data, the WLTP CO2 emission levels of 2018 vehicles are, on average, about 21% higher than the respective NEDC values. A similar analysis of an alternative dataset for 158 passenger cars shows the same result, indicating that WLTP CO2 levels are on average about 21% higher than NEDC CO2 levels.
Real-world refueling records for WLTP type-approved vehicles show a CO2 gap of 14% compared to the type-approval value. This is compared to a high of around 40% for NEDC type-approved vehicles. In other words, WLTP type-approved vehicles from the year 2018, on average, emit about 14% more CO2 under real-world driving conditions than suggested by the official WLTP figures and therefore come with a significantly more realistic indication of their behavior than NEDC type-approved vehicles of the same year.
However, due to the small amount of data available in 2018, these results should be regarded only as preliminary findings and should not be extrapolated to future years. It also is likely that the observed average WLTP-NEDC CO2 ratio and the average real-world gap will notably change for vehicles type-approved from 2019 onward due to a revision of the WLTP-NEDC correlation procedure, as well as provisions in the post-2020 CO2 standards, aiming to close earlier regulatory loopholes that allowed and may have incentivized manufacturers to artificially increase the WLTP-NEDC CO2 ratio.
Based on this analysis, policymakers should take a number of steps to ensure CO2 emissions are controlled as the regulations intended. These include:
Increasing data transparency by making both the measured and declared CO2 values of vehicles publicly accessible.
Continuing to monitor type-approval NEDC and WLTP values and closely scrutinizing the underlying reasons for the observed WLTP-NEDC CO2 ratio.
Implementing correction mechanisms that would lower a manufacturer target value from 2021 onward in case an intentional inflation of the WLTP-NEDC CO2 ratio is observed.
Ensuring real-word CO2 reduction by assessing how data from fuel consumption meters may be used to prevent the real-world gap from growing, and the feasibility of adjusting each manufacturer’s average CO2 emissions to its real-world performance.
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